Vortex lattice method

About: Vortex lattice method is a research topic. Over the lifetime, 779 publications have been published within this topic receiving 9242 citations.

High Fidelity Modelling for High Altitude Long Endurance Solar Powered Aircraft

Abstract: High Altitude Long Endurance (HALE) platforms are the aerial platforms capable of flying in the stratosphere for long periods of time. This master thesis presents aircraft system identification procedures geared towards such fixed wing platforms where aerodynamic forces and moments are parametrically modelled with so-called stability and control derivatives. The first part of the thesis addresses local System identification procedures intended for controller synthesis at low altitude flights whereas the second part of the thesis deals with a preliminary study on a new global system identification method. The local system identification procedure is based on the two step method, which offers flexibility regarding the aerodynamic structure. Therefore, it is suitable for the development of a system identification tool chain for various fixed wing platforms. Various system identification experiments have been conducted to collect flight test data. The parameters for the estimation of aerodynamic forces and moments are then found through an optimization procedure. Such parameters have been validated using a validation set from flight test data and their applicability for controller synthesis has been demonstrated. Global system identification typically requires the collection of flight test data at multiple points in the flight envelope and often, is combined with extensive Computational Fluid Dynamics (CFD) solutions as well as wind-tunnel experiments. Such an approach is time consuming and costly. This thesis presents a new method to overcome the limitations of the current methodology by applying a Parameter search on VLM-based (Vortex Lattice Method) dynamic simulations of aircraft System identification manoeuvres and correcting the estimated models with available flight test data. The current study shows improvements in fidelity with decrease in Root Mean Squared Error (RMSE) by factor 0.2 and 0.5 for x-axis and z-axis forces in body frame respectively, while reducing the effort for obtaining a model with similar fidelity.

Extended applications of the vortex lattice method

Abstract: The application of the vortex lattice method to problems not usually dealt with by this technique is considered It is shown that if the discrete vortex lattice is considered as an approximation to surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vortex-induced velocity that renders the vortex lattice method valid for supersonic flow Special schemes for simulating non-zero thickness lifting surfaces and fusiform bodies with vortex lattice elements are presented Thickness effects of wing-like components are simulated by a double vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentric cylindrical surfaces Numerical considerations peculiar to the application of these techniques are briefly discussed

An experimental and numerical study of FSI applied to sail yacht flexible hydrofoil with large deformations

Abstract: The recent use of large aspect ratio and highly loaded composite hydrofoils on sailing boats illustrates the limit of the assumption of rigid body. When flying, the hydrofoil presents large deformations which impact significantly the hydrodynamic loads expected. The present work focuses on an experimental campaign performed on a trapezoidal hydrofoil, made of polyacetate material, in the hydrodynamic tunnel at the Research Institute of French Naval Academy. Large deformations up to 4.5% of the span on the hydrofoil's tip are measured at angle of incidence 10° for Re=0.7x106 calculated at mean chord. Vibration analysis performed on this foil, highlights an increase of its resonance frequencies with bending loading. A coupled approach between the Vortex Lattice Method (VLM) potential flow code, AVL, for inviscid calculations, corrected to consider the viscous component and, an in-house structural code based on beam theory by Finite Element Method (FEM) is developed for this application. The comparisons of simulations show good agreements with experiments in a large range of angles of incidence and flow velocities.

Computer program for calculating aerodynamic characteristics of upper-surface-blowing and over-wing-blowing configurations

Abstract: The program is based on the inviscid wing-jet interaction theory of Lan and Campbell, and the jet entrainment theory of Lan. In the interaction theory, the flow perturbations are computed both inside and outside the jet, separately, and then matched on the jet surface to satisfy the jet boundary conditions. The jet Mach number is allowed to be different from the free stream value (Mach number nonuniformity). These jet boundary conditions require that the static pressure be continuous across the jet surface which must always remain as a stream surface. These conditions, as well as the wing-surface tangency condition, are satisified only in the linearized sense. The detailed formulation of these boundary conditions is based on the quasi-vortex-lattice method of Lan.